Surgical navigation systems, also known as computer assisted surgery and image guided surgery, aid surgeons in locating patient anatomical structures, guiding surgical instruments, and implanting medical devices with a high degree of accuracy. Surgical navigation has been compared to a global positioning system that aids vehicle operators to navigate the earth. A surgical navigation system typically includes a computer, a tracking system, and patient anatomical information. The patient anatomical information can be obtained by using an imaging mode such as fluoroscopy, computer tomography (CT) or by simply defining the location of patient anatomy with the surgical navigation system. Surgical navigation systems can be used for a wide variety of surgeries to improve patient outcomes.
To successfully implant a medical device, surgical navigation systems often employ various forms of computing technology, as well as utilize intelligent instruments, digital touch devices, and advanced 3-D visualization software programs. All of these components enable surgeons to perform a wide variety of standard and minimally invasive surgical procedures and techniques. Moreover, these systems allow surgeons to more accurately plan, track and navigate the placement of instruments and implants relative to a patient's body, as well as conduct pre-operative and intra-operative body imaging.
To accomplish the accurate planning, tracking and navigation of surgical instruments, tools and/or medical devices during a surgical procedure utilizing surgical navigation, surgeons often use “tracking arrays” that are coupled to the surgical components. The tracking arrays allow the surgeon to accurately track the location of these surgical components, as well as the patient's bones during the surgery. By knowing the physical location of the tracking array, the software detection program of the tracking system is able to calculate the position of the tracked component relative to a surgical plan image.
In a total knee arthroplasty (“TKA”) procedure to replace a worn or damaged knee, a significant amount of effort is devoted to ensuring that the resulting knee joint will be balanced. This balancing procedure is referred to as “soft tissue balancing.” Balancing may involve releasing the medial or collateral ligaments to correct for a varus or valgus deformity, such that the anatomical axis of the knee is correct when equal forces are applied to both collateral ligaments. A balanced knee joint will demonstrate proper ligament tension through the full range of motion, which provides a natural acting joint and minimizes pain and discomfort. Further, properly balanced ligaments reduce stress, wear and tear on the prosthesis and extend its life.
Soft tissue balancing is an imprecise art because there are few ways to precisely quantify the true tension of the ligaments, and this is further complicated by the pathology of arthritis. The amount of true contracture of the knee ligaments and the associated amount of soft tissue releasing required to obtain a “balanced” knee is often uncertain. It is known to use various distraction or “tensor” devices that have members that push the tibia apart from the femoral condyles with a known or pre-determined force, thereby applying the known force to the collateral ligaments. These tensors are often applied only after the bone cuts are complete, however, and are thus used as no more than a check on bone cuts that have been made from standard resection procedures.
Soft tissue balancing represents one of the major unsolved problems in knee surgery, and there is considerable interest in developing tools to assist with this process, especially in surgical navigation procedures.